Honing machines conventionally include a base on which a spindle head is mounted for reciprocally driven movement. A rotatable spindle mounted on the head rotates a honing tool which includes stones for performing the honing operation. Movement of the head from a withdrawn position to an operating position locates the tool within the bore to be machined whereupon the stones of the tool are expanded to perform the honing operation. Rotation of the tool by the spindle and concomitant reciprocal movement of the head on which the spindle is supported provides the stones with both rotational and axial movement during the machining is completed and withdrawal of the spindle head allows the machined part to be removed in preparation for another cycle.
Honing is usually utilized after a boring operation to accurately machine the bore and correct inaccuracies in the straightness or roundness as well as providing a smooth surface finish. Usually the amount of material stock removed is not particularly great; but, certain honing operations are performed with relatively coarse stones so as to greatly increase the size of the bore.
One type of honing machine incorporates a hydraulic feed cylinder for actuating expansion of the honing tool stones during the honing operation. Expansion of the stones is thus dependent on the pressure of the hydraulic fluid supplied to the feed cylinder. Resistance to the machining at the interfaces of the stones and the bore can slow or completely stop the stone expansion. For example, if the stones become glazed before the honing is completed, the pressure supplied to the feed cylinder may not be great enough to actuate the outward stone expansion so that the machining can be completed.
Honing machines which incorporate hydraulic fluid actuated feed cylinders are disclosed by U.S. Pat. Nos. 2,317,079; 2,333,256; 2,741,071; 2,787,865; 2,787,866; and 3,352,067.
Honing machines have also incorporated temperature sensing to sense the heat generated during the honing in order to control the pressure applied to the stones for actuating their expansion. See for example U.S. Pat. Nos. 2,191,256 and 3,287,860. Also, U.S. Pat. No. 3,404,490 discloses a honing machine having an electrical circuit that senses the resistance to stone expansion and varies the expansion force applied to the stones by an electric motor expansion mechanism.
U.S. Pat. Nos. 3,286,409 and 4,044,508 disclose single spindle honing machines having feed actuators for providing an initial fast stone expansion that engages the stones with the bore surface to be honed and a subsequent slower stone expansion as the machining takes place.
U.S. Pat. No. 3,849,940 discloses a honing machine having a pressure feed cylinder and a constant rate feed mechanism for providing stone expansion depending upon which has the higher feed rate as the machining takes plce. Also, single spindle honing machines have incorporated a pressure feed cylinder that is locked after the initial stone expansion so that a constant rate feed mechanism can subsequently expand the stones. Locking takes place at a connector that extends between the cylinder and the honing tool. A threaded connection of the connector is then unthreaded by the constant rate feed mechanism to expand the stones at a constant rate.
Stones of different coarseness are used to perform coarse and finishing honing operations. Usually the coarse stones are mounted on one honing tool and the finer stones are mounted on another tool. However, coarse and fine stones have also been mounted on the same tool and selectively expanded and contracted to first perform the coarse honing operation and subsequently perform the finer honing operation which finishes the bore. See U.S. Pat. No. 3,496,678.
Multiple spindle honing machines are used to simultaneously hone a plurality of bores such as, for example, the bores of an engine block. Different bores of the engine block will normally have different initial sizes so that the time required to hone the bores to the same size will vary.